BLE (or Bluetooth Low Energy) is a wireless personal area network technology designed, first of all, for data transmission.
BLE is not designed for positioning. Like any other RSSI-based (radio signal strength indicator) system, for example, WiFi, positioning is just a nice by-product for them. Yes, BLE does data transmission between phones, hands-free, etc.; it can also be used for tracking. In addition. With serious trade-offs.
It is the most vital point of RSSI-based technologies and its weakest point.
You don’t have an additional mobile beacon to track your location. Typically, your mobile phone or tablet, or similar gadget already has a BLE module, and by adding a particular SW/app to your device, you can track your mobile phone/tablet/gadget
RSSI is a very poor indicator of distance. The system may recover the location only because the SW is smart. But even with the best tricks, you shall realistically expect to know the location with 2-5m accuracy, if beacons are placed every 10-30m
BLE can be more complex and more advanced and support Angle of Arrival (AoA) and Angle of Departure (AoD)
When you need room-level accuracy and already have a mobile device with BLE onboard, the BLE RTLS is a good choice. This is an ideal case. Typical applications:
You place BLE beacons every 10-30m inside your premises. The beacons are small and can be easily camouflaged. For example, they emit Bluetooth signals once per second, and with this location update rate, they can run on an internal battery for one year or so. After one year, you change the battery on all of them.
You use mobile phones as your mobile trackers don’t need any changes or add-ons. They run an application that communicates with stationary beacons and calculates their position based on the radio signal strength of particular stationary BLE beacons and their known position. Everything works very well, albeit not too precise – 2-5m typically, which is OK for many applications (see examples above) but not for most industrial applications.
A typical requirement for people tracking in industrial applications is better than 1m. Often – better than 0.5m. BLE is not capable in the practice of providing such accuracy, or you need to place the BLE stationary beacons very densely – every 2-5m.
When we receive requirements about an indoor positioning system, potential customers often highlight that they have metal around. We immediately know they have probably burnt their feet with RSSI-based systems, typically BLE. Why? How do we know?
Well, as already discussed above, the RSSI-based indoor positioning systems use radio signal strength from a stationary beacon to the mobile beacon to estimate the distance. Yes, the farther your mobile beacon (phone) is from your stationary BLE beacon, the weaken the signal shall be. In practice, however, the RSSI fluctuates so drastically that the same RSSI may be measured on 2m and 10m. What distance is then?!
Everything is more or less OK when you have nice and empty space of airports or shopping malls full of radio-transparent glass or thin walls. But when you want to go to a packed warehouse full of metal shelves, palettes, forklifts, or other heavy machinery, the RSSI picture changes so drastically that the BLE-based tracking does not work with acceptable accuracy. Like really doesn’t work. You can be on this aisle or one or another. And what is the point in the system if you can not find what you want?
There is not only metal in the industrial environment but moving metal. Imagine you are not moving, but a forklift is moving 5m from you. But your location measured by the BLE-based system jumps. Why? Well, it happens because of multipath fading. Thus, a system calibration you did one hour ago may immediately become invalid.
Of course, smart algorithms try to recover somehow and re-calibrate the system. But in the end, it does not work well in the real industrial environment. RSSI-based systems are not designed for that kind of environment.
Life looks cool when you track mobile phones: download an app, and you are tracked. But what do you need to track, not a phone, but something else? Helmet? Crane? Palette? Forklift? – you need to install a mobile beacon on it—just another device. Well, for precise indoor positioning systems, you always need a mobile beacon, but they are accurate, at least. With this situation, you have both (1) poor accuracy and (2) additional mobile beacon with all difficulties of charging, additional costs, etc. One of the most decisive advantages – not requiring a separate mobile beacon for tracking – disappears from BLE systems in an industrial environment.
There are two major technologies recommended for industrial indoor positioning systems:
As discussed in the Review and comparison of indoor positioning technologies and methods focusing on industrial applications, both technologies rely on the time of flight – not on RSSI. That is the key advantage because it does not matter what is around: metal, concrete, wood, or nothing at all. UWB – time of flight of radio wave. Ultrasound – time of flight of ultrasound. Since the speed of sound is a million times slower than radio waves, ultrasound-based solutions are inherently far more accurate than UWB.
Therefore, the key practical advantages:
Of course, like for any precise indoor positioning system, line of sight is a must, but the definitions of what exactly “line of sight” is different:
Well, indoor optical positioning is not good in practice in an industrial environment. Devil is in detail:
LIDARs are not suitable for the majority of industrial positioning systems: